Reduction of fading effects in radio communication



Qct. 11,` 1932.

REDUCTION oF Filed July 28, 1928 A. H. TAYLOR ET AL FADING EFFECTS IN RADIO COMMUNICATION 2 Sheets-Sheet 1 AT ORNEY Oct. 11, 1932. A. H. TAYLOR ET AL 1,882,166

REDUCTION OF FADING EFFECTS IN RADIO COMMUNICATION MGM/f 3 5143604?, @ad Q,

sa- E Patented Get. 11, 1932 UNITED STATES PATENT-OFFICE ALBERT H. TAYLOR- AND LEO C. YOUNG, OF' WASHINGTON, DISTRICT OF COLUMBIA,

ASSIGNORSBY MIEISIN'? ASSIGNMENTS, T0 WIRED RADIO, INC.','OF NEW YORK, N. Y., l.Ay

CORPORATION OE' DELAWARE REDUCTION FADING EFFECTS IN RADIO COMMUNICATION x VApplication led July 28,

Qur invention relatesbroadly to radio receiving apparatus and more particularly to a systemfor reducing fading effects in radio communication.

One of thev objects of our invention is to provide a receiving System which automatically compensates for fading eifectsmaintaining signal strength at the receiver substantially constant. l

Another object of our invention is to provide an arrangement of superheterodyne circuits which cooperatively act to receive and reproduce signals independent of fading effects.

Other and further objects ofour invention reside in the superheterodyne circuit arrangements and proportion of the circuits as set forth more particularly in th-e specification hereinafter following byreference to the accompanying drawings in which:

Figure 1 is a diagrammatic view showing the arrangement of the superheterodyne apparatus at the receiver; Fig. 2 is a diagrammatic circuit arrangement of the two superheterodyne circuit arrangements of our invention; and Fig. 8 shows the detailsof the wiring of the apparatus in accordance with our invention.

In Letters Patent No. 1,669,218, issued May 8, 1928, to Albert H. Taylor, it has been pointed out that fading usually `occurs at dierent time intervals on antennas which are separated more than 1A of a wave length from the center ofone exposure to the center of the other, or which'run in diderent directions so as to be differently iniiuenced by different states of polarization in the changing wave front. A system of using two receivers with a common heterodyne is described in the aforesaid Letters Patent. That system had the disadvantage that vthe resultcould not be directly combined with the signal from the other receiver without vector addition of the signal so taking place in the operators telephones that the result, mathelnatically speaking, wouldV be the same as if only one antenna had been used.- v V In Letters Patent No. 1,669,219, issued May 8, 1928, to Albert Taylor, another-,system ing audio frequency signal from one receiver 192s. serial N0. 295,968.

was described in which two receivers are prov vided with two heterodynes'bringing the signals` to different audible frequencies which can therefore be combined by means of a differential transformer. This later system has the disadvantage of requiring filters to take up the resulting beat frequency between the two heterodynes, which will be within audible beat frequency of each other. The two previously described systems have in each of them certain disadvantages, although both systems assist in the reduction of fading effects. v n i The receiving system of our invention permits the two'signals, from the two 'collectors differently situated and spaced, to be received simultaneously. The receiving system of our inventionl also eliminates the objectionable beat notes which require filters betweenV the twoy heterodynes to eliminate these beats. The present receiving system of our invention is an improvement on either of the other systems referred to. Better results are accomplished in our present system by employing in combination the differentialy transformerI and two specially arranged superheterodyne receivers whichv are operated in a special manner with regard to the choice of the transfer frequencies.

The system can be understood by detailed reference to the drawings. Figfl shows an arrangement of the superheterodyne receiver for continuous wave reception but which will work equally well for reception of modulated signals by preventing oscillations of the second detector. The receiving system of our invention operates both klwith continuous wave signals and also in the reception of modulated signals of voice frequencies. The superheterodyne circuit arrangement includes a first detector 1 whose frequency characteristics correspond to the frequency of the incoming signal. By means of a heter- `odyne or driver 2 having frequency characteristics differing from the incomingv signal and loosely coupled to detector 1, the signal is transferred at adifferent andlower frequency through an amplifier and transfer circuit 3 and delivered to a second detector 4 whichhas frequency characteristics-corremay be antennas positioned ^infanteast and fit) Vor audio frequency ainplilier-circuits.

Referring to Fig. 2 let us suppose that col! lector A is dierently arranged 1n `space referenttinie jperiod of fading,` due jto `,selecting a slightly different portion ofthe wave front, or due to the two collectors being differently affected by differentpo-larization ofthe 'Wave front. As an illustration, collectors A and B west plane running in opposite directions and separated bya distance of about 100 meters.

Thei centers of exposure of these antennas wouldtherefore be 100 meters apart. These particularcollectors would respond similarly to varying states -of" polarization y,butv .each one would 'operate upon a slightly dierent portion ,ofVv the' down-coming waves. In the case of frequency characteristicsbetween l2,-

'000 and 22,000kilocy'cles, there would be severalwave lengths between the centers of exposure ofthe two'systeins. However, this effeet' in the Vreduction of fading begins with much less separation between thev centers lof exposure."` As another illustration, antennasA and inayjbe in the saine 'horizontal plane and at rightA angles to each other. 'An'- tennfas A and B would not only-.have different centers ofexposurelbut respond to VdifferentV polarization planes.VA iA- varietyof combina* tiens maybe used elfectively,fson`ie combinations worl'ring well at certain frequencies and on certain signals and others being prefer# "able for lother frequencies freniA other direc# tons. 4^ f If two identicalsuperheterodynes marked Super Het A and Super Het B are used in thelarrangernentshown in. Fig. 2'it will not be possible to get'the desired results. the first place, ifthetransfer frequencies are @the saine the oscillations' of the twov second detectors will` produce an audible beat and unless` very carefully filtered' will interfere 'with' each other. 'The filtering of these oscillations is not impossible but is rendered more difficult by `the, fact'that the two .outputf' circuits are :interconnected through the connnon differential transform:- ers. .Further the two beating heterodynes which transfer the signal-froml its original high frequency vforni tothe intermediate transfer vfrequency willfhave tobe absolutely synchronized' or they will produce audible beat frequencies. `This is extremely difcult when lthe frequencies are in the". order of 12,000 kilocycles or Y higher. Finally, if the oscillators andheterodynes are synchronized vector'additionsof the receiving signals will 'occur' instead of arithinetic additions and theefect willv be Vthe saine' as thoughone superheterodyne hadbeen used and ytheftfwo yheterodyne receiver.

collectors lcombined on entering the superi This' means that no material reduction in fading would result.

lt is obvious therefore, that if two identical superheterodynes f were usedY thev vvsystem yivould lack advantages,"but by combining two separate y superheterodynes y,having unlike characteristics;a` reduction in fading f phenomena; Ion these highen vfrequencies is possible. y

The first step is tocause the beating heteroy ifdynesfrequencies to differby angarnount sufficient to cause the resultant beating frequency' to bea'beyethe range of audibility. my frequency litteram? above 10i. @1005- lc'les ,between the Vtwo "beating heterdynes willfsuiielto; meet this condition but too great asepar'ationv should not occunfW hen the two heterodynes, forinstance, are caused to differ 500 lrilocycles', which vis jquite passible. in 'thereception of signals having frequencies ofthe ord'er of 20,000 kilocycles, the20th 'harmonie4 of the two theterodynes causes a beat frequency inthe signalling r ange. '.,Wth weak signals this' beating frequencyinight bestrong enough to cause'objectionable. interferencei` `By employing beat dierences between Vthetwo vheterodynes ofthe order of l0 to 50lrilocycles a very high'.'order of harmonics would be required tofca'usebeat frequencies within the signal range, andV such beatfrequencies are so weak as to vbe'V entirelyfnegligible.' As an (illustration,' suppese'we choose thedilference between v the two .beating he'terodyne frequencies'20'kilocycles.' This ineans in turn,'that Vthe transferfrequencies Iof the two heterodynes will differ-by Q'Olrilocycles. l'There is a wide variety possible in the choice of these transfer V.f'requencies'Y and the above' frequency is .inerelyfan illustration. It is convenient toE choosethe'f transferl frequency for superheterodyne approximately 100 lrilocycles andY forjsuperheterodyne `B", intheexainple cited, "-1120 kilocycles. Thesignal fromcollector A isf-thereforev transferred to oscillatingsecond--detector 1 ata frequency of 100 l'rilocycles where the audio frequency signal is produced oscillating 'p second detector l which inay have a'frequency difference of 870.0 kilocycles. The signal from collector B is transferred to superheterodyne B at a vfrequency'ofj 120 lrilocycles, requiring for an audible beat that .the second detector of superhet'erodyne be oscillated at a frequency oft 120 Vlrilocycles' 2*: anfaudible frequency. We cancause thesecond audibleV frequency to be identical with the first one if we desire to dogso, butfsifsuch is thecase vector addition lof thev signals-would resultv and not d reduction of fading. AV reduction offading is possible however :if we cause the audible beatfrequenciesjt be different, one 800 cycles the other .1200 cycles. Supposethat 'the incoming'signavlvhas afre'quency value of 20,000 kilocycles. Bot-h first detector (circuits for superheterodynes AA and B are tuned to this frequency value. The beating heterodyne for the superheterodyne A is adjusted to a frequency value of 20,100 kilocyeles. The beating heterodyne for superheterodyne B is adjusted toa frequency value of 20,120 kilocycles. vUnder these conditions no beat frequencies between these two heterodyne frequencies are of sufficient strength toV cause noticeable interference withreception. The oscillating second detector of `superheterodynewA is adjusted Ato a frequency `value of 100.8 lrilocyeles;v the Voscillating second detector of superheterodyne B is adjusted to a frequency value ofv 121.2 kilocycles. There is therefore no interfering beat frequency causedy by the two oscillating second detectors. As shown in F ig. 2, the output of superheterodynes A and B is connected to transformer 6 by means of primary windings 7 and 8. Secondary winding 9 is connected to telephones 5 or may be connected to other audio amplifiers. Transformer 6 need not be of the differential type as any three winding transformer with 'suitable impedance ratio will give Vsatisfactory results. Since the two signals can be brought in at two different audio frequencies and adjusted to cause a harmonious chord Vnot-annoying to the operator, the action of the fading, which is different on the two collectors, is emphasized alternately on the upper or the lower audio frequencies of the two.

The schematic circuitdiagramof the receiving system of ourA invention is illustrated more in detail in Fig. 3. Two complete receiving systems A and B are illustrated.

In receiver A, Va radio frequency energy collector orr antenna 27 transfers the incoming signal energy to the input circuit 28 of regenerative detector 12. A source of high frequency energy 11 is coupled to input circuit 28 ofthermionic vacuum tube detector 12. The beat frequency caused by the source of high frequency oscillations and the source of incoming signalling energy, is ampli-fied by thermionic vacuum tube 13, amplifier 14 and amplifier-detector V15. The second detector 15 which is an oscillating detector is adjusted to a frequency value whereby an audible beat frequency is produced. The audio beat frequency is amplified by ampliiier 16 and reproduced in circuits 7, 9 and 5. In receiver B a radio frequency energy collector or antenna 29 transfers the incoming signal energy to the input circuit 30 of regenerative rst detector 18. A source of high frequency energy 17 is coupled to input circuit 30 of thermionic vacuum tube detector 18. The source of incoming high frequency energy has a frequency value corresponding to the frequency value of the energy collected by antenna 27 and transferred to input circuit 2,8. Input circuit 30 is adjusted yto a frequency value corresponding to the frequency value .of input circuit 28. A source of high frequency energy 17 having frequency .characteristics unlike source 411, is coupled to input circuit 30. rIhe beat frequency energy, caused by the 'incoming` signalv and locally generated high frequency energy, is amplified by thermionic vacuum tube 19, amplifier 20 and amplifier-detector 21. The second detector 21 which is an osthe-reforebe beat frequencies oftwo differf ent frequency values in circuits 9 and 5. Sources of potential 25, 26, 28 yand 2a are illustrated as batteries. It is obvious that any suitable'supply may be employed. Thermionic vacuum tubes 13andv 19 are illustrated as of the shielding plate type, although it is also obvious that three electrode tubes may `be employed.V l/Ve Vrealize that many modifications of our invention are possible without `departing from thespirit of 1.;

our inventionand it is to be understood that our invention is not to` be restricted by the foregoing `specification or the accompanying drawings but only Vas delined in the scope of the appended claims. V, l

VJhat we claim as new and desire tojsecure by Letters Patent of the United Statesis as follows: v A,

1;. -A radio receiving system comprisingV in combination independentv radio frequency energy collecting circuits, .independent receiving circuits connected to said collecting circuits, a plurality of independent high frequency generators, each having frequency characteristicsV differingfrom the .other b v`` i a super-audible frequency, each of said receiving circuitsbeing adapted to heterodyne with at least one of said high frequency generators to produce super-audible beat frequencies and reproducing means common to each of i said last mentioned circuits. Y

. 2. rIhe method of receiving wirelessjsignals with geographically separated antennae which consists in receiving` the same signall upon each of a pair of said antennae to prol duce a pair of signal effects, independently heterodyning each of said signal effects to produce an intermediate frequency differing from that ofthe other, fixing the frequencies with which said signal effects are heterodyned so that the propagation ofan audible beat rfrequency therebetween is avoided, independently amplifying and detecting each of said intermediate frequenciesto produce an audio frequency differing from that of the other rodu'cindineansres onsive tosaid com Os! o K p and combining said audio frequencies, where..- by the effects of fading are substantially i'e- 8. An apparatusfor the elimination of fading comprising a plurality of spaced antennae each adapted to receive the 'same signal effect, an independent heterodyne receiving network connecting respectively witheach of said antennae, means associated with each of saidreceiving networks to produce an :interme-` diate ,frequency differentfrom that ofthe other, said means-being so relatedrtoone another inthe respective networks asA to avoid the direct propagation of an audible beat note therebetween,means included in each receiving network to independently amplify and detect each said intermediate frequency so as'to'produce an audio frequency in one said network dierent from that of the other,

means for combining said audio frequencies to produce a composite signal eect, and reite` signalv effect.

` il. The method of ,receiving wireless signals in a combining circuit 'with geographiq 'cally separated antennae which consists in` receiving the same signal upon each of-'a plurality of said antennae-and producing a plurality of signal-effects thereon,ydirecting Vthe energy from each lof said antennae to sepvaratereceiving' systems, producingv a super'- audible beat frequency diiierent in character A in each of said systems while avoiding the 1 per-audible frequency dier'ence between theV propagation of an audio-frequency-beat note as between the oscillatoryV characteristics of the respective systems by maintaining aV surespective beat frequencies, separably amplifying the beat frequency produced in each of said systems', separately detecting the separatebeat frequencies, and" producing separate audio frequencies in said receivers and combining the separate audio frequencies in the combining circuit whereby the effects of fading are substantially eliminated. A

' 5. An apparatus for the elimination of fad- A ing comprising a pluralityof antennae each having different instantaneous'fading charf acteristics, a separate superheterodyne receiver coupled to each of said antennae, means for producing different output frequencies from said receivers for the-same received signal, said means includingoscillators thefre- :6. An apparatus for the elimination of lfading comprising a plurality of geographically spaced antennae eacli 'having different Vinstantaneous fading 'characteristics and 'adapt'- edeach to receive the same signal energy,

a separate receiver connected :with each said antenna, means for.- producing aV different 3 radioy frequency heterodyne beat iiote on the saine signal with each `receiveigfsaid .means including oscillators the frequencies of which are-so fixed as to.' avoid audio-beat-frequency heterodyning .with one another, Va 'selective radiofrequency amplifier associated with the output of each of saidreceivers forv amplify-V ing the separate beat frequencies, a separate detector connected with .the output of each said amplifier and a receiving instrumentality for combining in one output circuit theaudio frequencies resulting Vfrom rectification by said rectifiers -whereby signals received -upon said geographically spaced antennae. have their energies added and combined in said receivinginstrumentality and the effects of tion -of an audio frequency beat note therebetween, the. frequencies. of said combining waves being differentat different ones'of-said places whereby' diiferent intermediate frequencies result from said lcombining actions,

separately detecting the signal component of eachsaid combining resultant waveand producing a relatively low frequency signal current in each of a pluralityof receiving systems and adding'said'waves of low'frequency to produce an audible signaling chord.

In testimony whereof we affix our signaquencies of which are so fiXedas to avoid v audio-beat-frequency lieterodyning with one another, independent selective intermediate frequency amplifiers inreacli receiver, a recti- Vfier coupled with the output ofeach said intermediate frequency amplifie-r, a common receiving instrumentality coupled to the output circuits of said-rectiiiers, whereby signals received upon said antennae are received in said receivingl instrumentality substantially unaii'ected by fadingand are combined into an harmonious chord ofir audio frequencies. 

